Frank Lampard admitted his Chelsea side were confronted with the "harsh reality" of the Premier League after the Blues succumbed to a heavy 4-0 defeat at Manchester United.
Chelsea's new head coach handed starts to Tammy Abraham and Mason Mount in a youthful line-up at Old Trafford and the homegrown pair started brightly, the former rattling a post when the score was still goalless.
The visitors arguably shaded the first half but trailed to a Marcus Rashford penalty before United ran riot after Anthony Martial had doubled their advantage shortly after the hour mark.
Rashford scored once more before debutant Daniel James netted to give the hosts victory by a margin that flattered them in both sides' curtain-raiser, something Lampard was keen to highlight.
Lampard said: "We were clearly the better team for 45 to maybe 60 minutes. What was evident was that we made individual errors which led to four goals out of their five shots (on target), there's the harsh reality for us.
"If we go in at half-time 2-1 or 3-1 up, as we probably should have done, if we were more clinical and had maybe a stroke of luck here and there, the game would be completely different.
"Football is won and lost in the boxes, they won in our box by being clinical.
"We had so many more shots than them and attacking entries and getting high up the pitch. That was where we let ourselves down in not putting the chances away.
"It's quite hard to talk about it after 4-0, you can sound stupid but anyone who watched the game would have seen that. We gave them clear opportunities to score and they took them."
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Injuries hurting Chelsea
Lampard was unable to start a number of regulars because of injury while the former midfielder has been hindered in recent months by Chelsea's transfer ban.
He added: "I can't drag people out of the medical room to play.
"Let's be clear with the injuries we have at the minute, with the fact we couldn't bring in players, this is going to be a work in progress to a degree. We will have to learn harsh lessons and correct them pretty quickly.
"There were lots and lots of elements to the game that I liked, there were four or five elements that I didn't like and they were fatal for us.
"We can't run away from the fact that we know where we're at, we couldn't bring in players, most managers at a club like Chelsea can bring in players to change the way they want to play, to bring in quality, etc.
"But we can't, I'm not going to complain too much about that, I want to work."
Manchester United manager Ole Gunnar Solskjaer admitted his side had their moments of fortune but was immensely satisfied by their fantastic start to the season.
He said: "You take a win because it's about points first. The second-half performance was very pleasing, that was the big plus coming into half-time because we were a bit lucky.
"They pinned us back created chances but we settled a few nerves.
"We're still a work in progress, we still know we're not anywhere near the finished article and we have got loads of improvement to be made.
"But we have found a way we want to play. We took risks but that's the way here, you've gotta go for it, risk and reward."